Defoamers are compositions used in the pulp and paper mill industry for the control of foam in various processes. In addition to the pulp and paper industry, defoamers are also useful in the petroleum industry, water treatment, paints and coatings, food and beverage processing, the mining industry, textiles, agriculture, and the like.
Foam control is a common industrial problem. As such, defoamers are being developed to alleviate this problem. Common defoamer compositions are generally composed of a carrier fluid, a defoaming agent and miscellaneous additives. Foaming problems often have been effectively dealt with by using various petroleum oil-based compositions containing an alkylene diamide and/or hydrophobic silica (silicone coated silica), as well as silicone emulsions and concentrates. Further, cost effective carrier fluids have often been the petroleum oils (mineral oils). Water is also often part of defoamer formulations. Various defoaming compositions have been documented in product literature and patents. See, e.g., U.S. Pat. Nos. 5,082,590; 5,096,617 and 5,071,591.
Oil-based amide defoamers contain a minimum of two ingredients: a wax with a high melting point and an oil carrier (usually derived from petroleum), in which the wax is dispersed. A commonly used wax class is the diamides. A common diamide is ethylene bis-stearamide (EBS), but other diamides or mixtures of diamides can also be found in defoamer blends. EBS is a very hydrophobic molecule that can have deposition potential if not formulated and used correctly. There have been instances where EBS has been found in unwanted deposits in pulp and paper mills. Deposition can lead to discontinuing introduction of defoaming agents that are believed to contribute to the deposition event.
The typical weight fraction of diamide is between about 2 and 10% of the composition whereas the weight fraction of the petroleum oil is often over 80%. The carrier oil varies in composition from one defoamer to another but generally consists of a low viscosity mineral oil with paraffinic or cycloparaffinic hydrocarbons. In addition to the diamides and petroleum oil, the blends may also contain other agents such as hydrophobic silica and silicone oil, various emulsifiers, and stabilizers, but these constituents generally comprise less than about 10% of the formulation.
While these diamide-based compositions are effective defoamers, they have been suspected of contributing to deposition problems in various locations in the mills. (Dorris et al. “Analysis of Amide Defoamers in Kraft Mill Pitch Deposits,” J. Pulp & Paper Science, 11:5, J149-J154, September 1985) There is some evidence that the petroleum oil in this type of defoamer can lead to undesirable by-products in Kraft bleach plants (Allen. et al. manuscript distributed at the 8th International Symposium on Chlorinated Dioxins and Related Compounds, Urnes, Sweden, Aug. 21-26, 1988) In addition, they can demonstrate limited performance efficiency on paper machines because they are not able to completely disperse in water thus they have potential to form deposits and/or oil spots in the paper produced.
Alternative petroleum oil-based defoamers have been prepared from a wide variety of chemicals. For example, U.S. Pat. Nos. 3,751,373 and 3,935,121 disclose defoamers based upon a combination of a fatty acid or alcohol, a polyethylene glycol mono- or di-ester of a fatty acid, a petroleum sulfonic acid, and an organic liquid.
An example of a commercial aqueous-based defoamer is an aqueous emulsion of fatty alcohols. Although the aqueous defoamer does not contain petroleum oil phase, it does however, contain high melting waxes which have been associated at times with undesired effects in processing. These defoamers are generally not as effective as those containing EBS and their homologues, but also do not cause the spotting problem on paper machines that are associated with formulations containing oil, EBS or silicone.
Silicone has commonly been implicated as a contributor to some deposition issues in various processing steps. If not properly formulated and applied, these materials can cause similar or the same problems as oil-containing defoamers. As a result, many pulp and paper mills avoid using silicone containing products.
Therefore there is a need for a cost effective and environmentally friendly defoamer formulation which does not contain oil, EBS or free silicone and performs as good as, if not better than pre-existing defoamers.